Load-alleviator hydrofoil unit for watercraft



Aug. 10, 1965 w. R. WIBERG LOAD-ALLEVIATOR HYDROFOIL UNIT FOR WATERCRAFT 2, Sheets-Sheet 1 Filed Oct. 19, 1964 INVENTOR. WALTER R. WIBERG Aug. 10, 1965 w. R. WIBERG 7 3,199,484

LOAD-ALLEVIATOR HYDROFOIL UNIT FOR WATERCRAFT Filed Oct. 19, 1964 2 Sheets-Sheet 2- INVENTOR. wAL TH? E. w/BERG United States Patent 3,l9,484 LQAQ'AIJIEVIATGR I IYDRGFGII. UNIT FUR WATERCRAFT Walter R. With-erg, Eleattle, Wash, assignor to The Boeing (Company, Seattle, Wash a corporation of Delaware Filed Get. 15 19nd, Ser. No. 464,817 Ill Claims. (Cl. lid-e65) This invention relates to hydrofoil units for watercraft and more particularly to load-alleviating hydrofoil units for watercraft.

The lifting surfaces or foils of hydrofoil units, whether of the submerged or surface-piercing type, experience incremental lift forces when operating in certain sea states. These forces are produced by the varying depth of the lifting surface below the surface of the water due to waves and the orbital velocities within a wave which together vary the instantaneous angle of attack and relative velociof the lifting surface with respect to the water. These actions produce vertical accelerations of the watercraft which if uncontrolled will limit the maximum wave height in which the craft can operate. One approach to controlling the incremental loads on the lifting sufrace has been the use of flaps or incidence control surfaces mounted on the lifting surface and actuated by an automatic control system which senses vehicle motions. However, these systems have proved to be very complex and expensive. Another attempt, indicated by the prior art, has been the use of a hydrofoil unit which is pivotally mounted through a shaft to the hull of a watercraft. Incremental loads experienced by the lifting surface of this hydrofoil unit are transmitted through a torque produced on the mounting shaft to a spring system which resists the mounting shaft rotation. Such system, however, provides a single suspension point for the hydrofoil unit thus requiring such mounting point to accept large loads. Moreover, the distance between the center-of-pressure on the lifting surface and the pivot point relative to the distance between the center-of-drag and the pivot point, makes a single mounting hydrofoil unit highly sensitive to drag forces rather than lift forces.

Accordingly, it is an object of the present invention to provide a load-alleviating hydrofoil unit for a watercraft which is mounted to the hull of a watercraft at two longitudinally spaced apart locations so as to change its angle of incidence in response to incremental loads on the hydrofoil unit lifting surfaces.

It is another object of the present invention to provide a load-alleviating hydrofoil unit for a watercraft which has a lifting surface supported by two arms one of which is pivotally mounted and the other being supported through reaction means longitudinally and laterally spaced apart from the pivotal mountin so that the unit is primarily responsive to incremental lift loads on the lifting surfaces.

For a better understanding of the invention, together with other objects thereof, reference should now be made to the following detailed description which is to be read in conjunction with the accompanying drawings in which:

FIGURE 1 is a side elevation view of a watercraft having a load-alleviating hydrofoil unit;

FIGURE 2 is a plan view of the watercraft shown in FIGURE 1;

FIGURE 3 is a front elevation view of the watercraft shown in FIGURE 1;

FIGURE 4 is a diagrammatic side elevation view of a portion of a watercraft having a modified load-alleviating hydrofoil unit;

FIGURE 5 is a diagrammatic plan view of the portion of the watercraft shown in FIGURE 4;

FIGURE 6 is a diagrammatic front view of the watercraft shown in FIGURE 4;

FIGURE 7 is a diagrammatic side elevation view of a watercraft having another modified load-alleviating hydrofoil unit;

FIGURE 8 is a diagrammatic plan view of the portion of the watercraft shown in FIGURE 7;

FIGURE 9 is a diagrammatic front view of the portion of the watercraft shown in FIGURE 7.

Referring now to FIGURE 1, there is shown a watercraft 2%) having a hull 22, a fixed angle-of-incidence rear hydrofoil unit 24, propulsion means 26 and a pair of loadalleviating hydrofoil units 28 and 30 mounted on opposite sides of hull 22. The hydrofoil unit configuration shown in FIGURES 1 through 3 is a zero-shift center-of-pressure system. In such a system, the center-of-pressure of the vertical forces which lift the watercraft is fixed irrespective of the depth of immersion of the hydrofoil in the water. In other words, the surface-piercing lifting surfaces of the hydrofoil unit are arranged in balanced manner so that the lift loads applied thereto do not shift longitudinally depending upon the depth to which the lifting surfaces are submerged. Since the hydrofoil units 28 and 30 are identical in structure, as well as operation, the following description will apply to only one of such units.

The surface-piercing load-alleviating hydrofoil unit 28 generally comprises a pair of supporting arms, a pair of surface-piercing lifting surfaces and reaction means. On the underside of bull 22 a pivotal mounting 32 is provided which supports one end of a supporting arm 34. The opposite end of arm 34 is fixedly connected to a surface-piercing lifting surface 36. Lifting surface 36 extends downwardly, rearwardly and outboard having its lower end fixedly connected to the lower end of a second lifting surface 38. Lifting surface 38 extends upwardly, rearwardly and outboard and has its upper end fixedly connected to a second arm 49. Arm 40 extends upward and inboard towards the bow of the watercraft and has its upper end carried by reaction means 42. Reaction means 42 comprises a housing 44 mounted on hull 22 and sl-idcably carries a shaft 46 having a pivotal housing 48. The upper end of a shock absorber 50 is pivotally mounted in housing 48 and the lower end is pivotaliy connected to a supporting plate 52. The upper end of arm 40 is fixedly connected to plate 52 and the latter also carries one end of stabilizer 54, the upper end of stabilizer 54 being pivotally mounted to hull 22.

In operation, incremental loads applied to the lifting surfaces due to the varying depth the lifting surfaces are submerged and to wave orbital velocities produce a rotation of the hydrofoil unit 28 about the pivotal mounting 32. It is apparent that such rotation causes a change in the angle of incidence of the lifting surfaces relative to the water. This change in incidence angle results in a decreased lift of the lifting surfaces 36 and 38 so as to mitigate any change in height of the watercraft relative to the water level which would otherwise occur due to the incremental loads. While the change in angle of incidence produces an immediate decrease in lift, the reaction system 42 tends to restore the lifting surfaces to their original positions to maintain the craft at its original level above the water surface. Since the necessary restoring force of system 42 depends on the longitudinal distance between pivotal mounting 32 and shock absorber 50 relative to the distance between mounting 32 and the center-of-pressure (c.p.), it will be seen that the twopoint mounting of the unit with the sweep-back of the lifting surfaces 36 and 38 provides a hydrofoil unit 28 with considerable mechanical advantage. Moreover, the lifting surface mounting arrangement and the lifting sur- .8 face sweep-back, provides a long moment arm for the center-of-pressure through which the lift forces act relative to the length of the leve through which the lifting surface drag acts,.thus making the unit more sensitive to lift forces.

It is to be understood that while the reaction means in the above-described hydrofoil unit is a passive system comprising a hydraulic shock absorber, other devices such as an air spring, a simple coil spring or a hydraulic accumulator could be used; furthermore, the reaction means could be an active system comprising an actuator responsive to motions of the watercraft.

It should also be noted that in this embodiment the pair of hydrofoil units 28 and 30 are connected by torsion bar 56, as seen best in FIGURE 3. In this manner, the hydrofoil units operate dependently so as to provide roll stability to the watercraft. The interconnection by torsion bar 56 could be provided by other devices, however, such as hydraulic linkage.

In FIGURES 4 through 6, an alternate embodiment of a load-alleviating hydrofoil unit is shown. The watercraft 76 comprises a hull 72 and a pair of load-alleviating surface-piercing hydrofoil units 74. One of the hydrofoil units 74, comprises a lifting surface 76 which is normally totally immersed in the water and extends substantially athwartship the longitudinal centerline of the watercraft. On the outboard end of lifting surface 76 a surface-piercing lifting surface 78 is fixedly connected which extends upward, aft and outboard relative to the lifting surface 76. The upper end of partial lifting surface 78 is fixedly connected to a first arm 80 at its lower end. The arm 80 extends upward, af-t and inboard and has its upper end supported by resilient suspension means 82. A second arm 84 is fixedly mounted to hull 72 and depends downwardly having its lower end pivotally connected to lifting surface 76.

In FIGURE there is illustrated the starboard plane view of the watercraft 70 shown in FIGURE 4. Sweepback lifting surface 76 is partly visible and partly hidden by the hull 72. The outboard end of lifting surface 76 is fixedly connected with the surface piercing lifting surface 78 which extends upwards from lifting surface 76 and aft and outboard relative to the watercraft 70.

A first arm 80 is fixedly connected with the upper end of the partial lifting surface 78 on one side and is supported by resilient suspension means 82 on the other side.

FIGURE 6 is a front view of the watercraft "itl illustrating the hydrofoil units 74 on port and starboard of watercraft 7i) and in particular shows the pivot 86 between lifting surface 76 and second arm 84.

Operation of this embodiment of a load-alleviating hydrofoil unit is identical to that of the embodiment shown in FIGURES 1 through 3. However, the modified embodiment constitutes an arrangement whereby the lift center will move aft with increased submergence of the surface-piercing lifting surface 78. This has the effect of further increasing the moment about pivot 86 and also increasing the reacting load on 82. In this manner the change in incidence with submergence will be further increased over the fixed center-of-pressure system.

Another embodiment of a load-alleviating surfacepiercing hydrofoil unit is shown in FIGURES 7 through 9. The watercraft 90 includes a hull 92 a pair of loadalleviating hydrofoil units 94. Each of the hydrofoil units 94 comprises a lifting surface 96 which is normally totally submerged in the water and a surface-piercing lifting surface 98 having its lower end fixedly attached to the outboard end of lifting surface 96. Partial lifting surface 98 extends upward, forward and outboard with respect to the lifting surface 96 and has its upper end fixedly connected to the lower end of an arm 11.90. The arm 1% extends inboard, forward and upward and has its upper end connected to hull 92 through pivotal mounting 102. A second arm 104 provides the second mounting means for the lifting surfaces and has its lower end fixedly mounted to lifting surface 96 and its upper end carried by a spring suspension system 196.

While the operation of this embodiment of a loadalleviating hydrofoil unit is the same as the previous embodiments, the center-of-pressure in this arrangement moves forward with increased immersion of the surfacepiercing lifting surface. This forward movement of the center-of-pressure decreases the amount of incidence change with submergence. In this manner the change in incidence with submergence will be less than obtained with a fixed center-of-pressure system.

It has been shown that the objects of this invention are accomplished irrespective of the particular arrangement of the hydrofoil unit providing that the lifting surfaces are supported by the watercraft hull at two locations, one of which is a pivotal mounting and the other of which is through a reaction means, and that these two points are widely spaced apart in a longitudinal direction. Also, while several embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects. Accordingly, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In a watercraft having a hull, a load-alleviating hydrofoil unit comprising:

(a) a sweepback foil having an aft sweep back portion and forward sweep back portion;

(b) reaction means responsive to movement of said foil and mounted on said hull;

(c) a first arm having one end connected to said reaction means and depending forwardly and downwardly, the other end of said arm fixedly connected to said foil after sweepback portion; and

(d) a second arm having one end fixedly connected to said hull and depending downwardly, the other end of said arm pivotally connected to said foil forward sweepback portion, said second arm connection to said hull being longitudinally and laterally spaced apart from said reaction means with respect to the longitudinal axis of said watercraft.

2. In a watercraft having a hull, a load-allevating hydrofoil unit comprising:

(a) a normally submerged lifting surface;

(b) a partially submerged lifting surface having its lower end attached to said submerged lifting surface and extending rearwardly and outwardly relative to said submerged lifting surface;

(c) a first arm attached at its lower end to the upper end of said partially submerged lifting surface and extending rearwardly and inwardly, the upper end of said first arm carried by a reaction means;

(d) a second arm pivotally attached to said submerged lifting surface at its lower end and extending upwardly, the upper end of said second arm fixedly mounted to said hull; and

(e) said reaction means mounted on said hull at a longitudinally and laterally spaced apart location from said fixed mounting of said second arm upper end, with respect to the longitudinal axis of the watercraft whereby incremental loads in an upwardly direction applied to said submerged and partially submerged lifting surfaces produce a change in the angle of incidence of said lifting surface.

3. The hydrofoil unit of claim 2 wherein said reaction means includes a resilient element.

4. The hydrofoil unit of said claim 2 wherein said reaction means comprises actuating means responsive to motion of the watercraft.

5. The hydrofoil unit of claim 2 wherein said reaction means is adjustable for various sea-state operating conditions.

6. In a watercraft having a hull, a load-alleviating hydrofoil unit comprising:

(a) a normally submerged lifting surface;

(b) a partially submerged lifting surface having its lower end attached to said submerged lifting surface and extending forwardly and outwardly relative to said submerged lifting surface;

(0) a first arm attached at its lower end to the upper end of said partially submerged lifting surface and extending forwardly and inwardly, the upper end of said first arm pivotally attached to said hull;

(d) a second arm fixedly attached to said submerged lifting surface at its lower end and extending upwardly, the upper end of said second arm carried by a reaction means mounted on said hull; and

(e) said reaction means mounted on said hull at a longitudinally spaced apart location from said pivotal attachment of said first arm upper end, whereby incremental loads in an upwardly direction applied to said submerged and partially submerged lifting surfaces produce a change in the angle of incidence of said lifting surfaces.

7. The hydrofoil unit of claim 6 wherein said reaction means includes a resilient element.

8. The hydrofoil unit of claim 6 wherein said reaction means comprises actuating means responsive to motion of the watercraft.

9. The hydrofoil unit of claim 6 wherein said reaction means is adjustable for various sea-state operating conditions.

10. In a watercraft having a hull, a load alleviating hydrofoil unit comprising:

(a) a pair of lifting surfaces, each having a forward portion and an athwartship end portion, said surfaces normally submerged and extending substantially athwartship;

(b) a pair of resilent suspension means mounted on the opposite side of said hull, each of said suspension means being disposed substantially vertically, the upper end of each of said suspension means being fixedly connected to said hull and the lower end of each of said suspension means being fixedly connected to the athwartship end portion of each of said lifting surfaces, and

(c) a pair of arms having upper and lower ends fixedly mounted at said upper ends to said hull at a substantially forward location with respect to said resilent suspension mounting means at said hull, the lower end of said arms pivotally supporting the forward portion of each of said lifting surfaces.

ii. The watercraft as claimed in claim 10 wherein said lifting surfaces have a V shaped plan view.

References Cited by the Examiner UNITED STATES PATENTS 2,991,747 7/61 Bader et al. 14466.5 3,104,642 9/63 Piazza 1l4-66.5

FOREIGN PATENTS 768,045 6/55 Germany.

MILTON BUCHLER, Primary Examiner.

FERGUS S. MIDDLETON, Examiner. 

1. IN A WATERCRAFT HAVING A HULL, A LOAD-ALLEVIATING HYDROFOIL UNIT COMPRISING: (A) A SWEEPBACK FOIL HAVING AN AFT SWEEP BACK PORTION AND FORWARD SWEEP BACK PORTION; (B) REACTION MEANS RESPONSIVE TO MOVEMENT OF SAID FOIL AND MOUNTED ON SAID HULL; (C) A FIRST ARM HAVING ONE END CONNECTED TO SAID REACTION MEANS AND DEPENDNG FORWARDLY AND DOWNWARDLY, THE OTHER END OF SAID ARM FIXEDLY CONNECTED TO SAID FOIL AFTER SWEEPBACK PORTION; AND 